1. Field of the Invention
The present invention relates to a circulating pump for pressurizing and circulating fluid in a system such as a boiler, and more particularly to a circulating pump for cooling water to be forcibly circulated in such a manner that fluid pressurized into an impeller chamber by an impeller flows through a spiral groove formed at the outer surface of a motor shaft and a cooling water discharging passage formed at the center of the motor shaft and returns into the impeller under a pressure difference between the impeller chamber and an inside of the impeller so that a motor of the circulating pump is cooled.
2. Description of the Prior Art
In general, a circulating pump is equipped in a system such as a boiler for circulating fluid under the action of pressure. Such a circulating pump conventionally comprises a motor acting as a power source for the circulating pump; an impeller which is combined with an output shaft of the motor, rotates together with the motor shaft according to the rotation of the motor shaft, and directly pressurizes fluid; and a pump housing which receives the impeller and includes an inlet passage for allowing fluid to flow into the impeller and an outlet passage for allowing fluid pressurized by the impeller to flow out of the impeller.
In such a prior-art circulating pump, fluid that has flowed into the pump housing through the inlet passage of the pump housing is pressurized by the impeller rotating according to the rotation of the motor and flows out of the pump housing through the outlet passage thereof.
FIG. 1 and FIG. 2 show one of the embodiments for the prior-art circulating pump as described above.
According to FIG. 1 and FIG. 2, a prior-art circulating pump 1 comprises a motor 10, an impeller 20 and a pump housing 30.
Motor 10 includes a stator 11, a rotor 12 and a motor shaft 13. Stator 11 is fixed inside a motor housing 14. Rotor 12 is fixedly assembled with motor shaft 13 and separated from stator 11 by a stator can 15. One end of motor shaft 13 is supported by a lower bearing holder 16a and a lower bush bearing 17a at the inner bottom of motor housing 14. The other end of motor shaft 13 passes through a motor end shield 18 and is supported by an upper bearing holder 16b and an upper bush bearing 17b at motor end shield 18. Motor shaft 13 is supported by a trust bearing 17c which is to keep the motor shaft 13 from rising in an axial direction of the motor shaft 13. Between lower bearing holder 16a and stator can 15, an O-ring 19a is provided to prevent fluid from leaking out. Likewise, an O-ring 19b prohibits the leakage of fluid between motor end shield 18 and stator can 15.
Impeller 20 includes an impeller body 21 and a shroud 22. Impeller body 21 and shroud 22 are, in general, connected to each other by an ultrasonic welding. Impeller body 21 is tightly fitted at the other end of motor shaft 13 by a bush 23. At the center of shroud 22 a through hole 24 is formed.
Pump housing 30 is disposed onto motor 10. Pump housing 30 includes an inlet passage 31 and an outlet passage 32 at its right and left sides respectively and an impeller chamber 33 at the center thereof. Impeller 20 is disposed inside impeller chamber 33. A suction ring 34 with a flange 34a and a cylinder 34b is provided at one end of inlet passage 31 of pump housing 30 just above shroud 22 of impeller 20. A fluid guide hole 35 is formed at the center of suction ring 34. Cylinder 34b of suction ring 34 protrudes with a predetermined length into through hole 24 formed at the center of shroud 22 of impeller 20. Between through hole 24 of shroud 22 and an outer wall of cylinder 34b of suction ring 34, and between an upper end of shroud 22 and a lower side of flange 34a of suction ring 34, some measure of clearance is provided. An O-ring 19c is provided to prevent fluid from leaking out between pump housing 30 and motor end shield 18.
According to the prior-art circulating pump constructed as above, when an electric current is applied to stator 11 of motor 10, motor shaft 13 which is rotatably supported against motor housing 14 by means of lower bush bearing 17a and upper bush bearing 17b rotates by an electromagnetic force occurring between stator 11 and rotor 12. Accordingly, impeller 20 which is tightly fitted at one end of motor shaft 13 by means of bush 23 rotates. When impeller 20 rotates, the fluid that has flowed into impeller 20 through inlet passage 31 and suction ring 34 of pump housing 30 is pressurized by impeller 20 and is delivered into impeller chamber 33 and subsequently to outlet passage 32. At this time, some of the pressurized fluid in impeller chamber 33 flows into stator can 15 through a gap between motor shaft 13 and upper bush bearing 17b. The fluid that has flowed into stator can 15 cools motor 10. The fluid which has entered stator can 15 reversely rises to flow into impeller chamber 33, and thereafter flows out of impeller chamber 33 together with other pressurized fluid therein through outlet passage 32.
However, according to the prior-art circulating pump constructed as above, since fluid that has flowed into stator can 15 through the gap between motor shaft 13 and upper bush bearing 17b is small in quantity, motor 10 can not be cooled satisfactorily. As such, since heat generated by friction between motor shaft 13 and bearings 17a, 17b and 17c is not sufficiently cooled, motor shaft 13 and bearings 17a, 17b and 17c are apt to be worn away earlier, and therefore the efficiency of pump 1 decreases and the expected life of pump 1 is shortened.
Also according to the prior-art circulating pump constructed as above, when a substance such as mud enters stator can 15 together with fluid through the gap between motor shaft 13 and upper bush bearing 17b, since the gap between motor shaft 13 and upper bush bearing 17b is quite narrow, the substance that has entered thereinto is hardly discharged to impeller chamber 33 again. That is, the substance remains in the stator can 15. At this time, if the substance gets in between motor shaft 13 and lower bush bearing 17a, a lubricative rotation of motor shaft 13 can be obstructed. Especially, if pump 1 is not used for a long time, the substance will solidify so the rotation of motor shaft 13 could be impossible.
FIG. 2 and FIG. 3 show a second embodiment for the prior-art circulating pump according to the "CIRCULATING PUMP" disclosed in a U.S. patent application based upon Korean patent application No. 18229/95 of the same inventor and simultaneously filed with the present application.
In accordance with FIGS. 2 and 3, a prior-art circulating pump 51 comprises a motor 60, an impeller 70 and a pump housing 80.
Motor 60 includes a motor housing 64. A stator 61 is fixed inside motor housing 64. Stator 61 is separated from fluid by a stator can 65, a motor end shield 68 and a plurality of O-rings 69a, 69b and 69c. A rotor 62 is fixedly assembled with a motor shaft 63. One end of motor shaft 63 is supported rotatably and slidably in an axial direction of the motor shaft 63 by a lower bearing holder 66a and a lower bush bearing 67a at the inner bottom of motor housing 64. The other end of motor shaft 63 passes through a through hole 68a formed at a motor end shield 68 and is supported rotatably and slidably in the axial direction by an upper bush bearing 67b at motor end shield 68. Between lower bearing holder 66a and stator can 65, O-ring 69a prohibits fluid from leaking out. Likewise, O-ring 69b prohibits fluid from leaking out between motor end shield 68 and stator can 65.
Impeller 70 includes an impeller body 71 and a shroud 72. Impeller body 71 and shroud 72 are connected to each other by an ultrasonic welding. Impeller body 71 has a plurality of blades 71a for pressurizing fluid and is fixedly assembled with the other end of motor shaft 63. One end of shroud 72 is tightly fixed onto impeller body 71, and at the center thereof a through hole 73 is formed. An inclined surface 73a is formed at an upper edge portion of through hole 73. At the other end of shroud 72, there is provided an annular flange 72a with a plurality of grooves 72b thereon.
Pump housing 80 is disposed onto motor 60. Pump housing 80 includes an inlet passage 81 and an outlet passage 82 provided at both sides thereof respectively and an impeller chamber 83 formed at the center thereof. Impeller 70 is disposed inside impeller chamber 83. Impeller chamber 83 is communicated with inlet passage 81 and outlet passage 82 respectively. A suction ring 84 is provided at one end of inlet passage 81. Suction ring 84 includes a flange 84a and an inclined guiding portion 84b with the same angle with an inclined surface 73a of shroud 72. Between pump housing 80 and motor end shield 68, O-ring 69c is provided to prevent fluid from leaking out.
According to the prior-art circulating pump constructed as above, when a current is applied to stator 61 of motor 60, motor shaft 63 which is rotatably supported against motor housing 64 by means of lower bush bearing 67a and upper bush bearing 67b rotates by an electromagnetic force occurring between stator 61 and rotor 62. Accordingly, impeller 70 which is tightly fitted at one end of motor shaft 63 rotates. When impeller 70 rotates, fluid flows into impeller 70 through inlet passage 81 and suction ring 84 of pump housing 80. The fluid is pressurized by rotating impeller 70 and is delivered into impeller chamber 83 and subsequently to outlet passage 82. When impeller 70 rotates, fluid that has flowed through inlet passage 81 thereinto is pressurized into impeller chamber 83 by a plurality of blades 71a of impeller 70, accordingly the fluid pressure in impeller chamber 83 is higher than that in an inside of impeller 70. Accordingly, impeller 70 is forced toward suction ring 84. Meanwhile, since motor shaft 63 at which impeller 70 is fixed is supported against motor housing 64 rotatably and slidably in the axial direction by lower bush bearing 67a and upper bush bearing 67b, impeller 70 axially rises toward suction ring 84 while rotating.
Further, since the fluid pressure in impeller chamber 83 is higher than that in the inside of impeller 70, the pressurized fluid in impeller chamber 83 is reversed to flow to inlet passage 81 through clearances between the upper side of annular flange 72a of shroud 72 and the lower side of flange 84a of suction ring 84 and between inclined surface 73a of shroud 72 and inclined guiding portion 84b of suction ring 84. At this time, the fluid that has flowed into the clearance between the upper side of annular flange 72a of shroud 72 and the lower side of flange 84a of suction ring 84 is affected by a centrifugal force going back toward the outside of annular flange 72a by a plurality of grooves on annular flange 72a. Fluid that has flowed into the clearance and fluid pressurized outward by grooves 72b conflict with each other around outer ends of grooves 72b. This fluid confliction makes a fluid film with considerable pressure between shroud 72 and suction ring 84. The fluid film serves as a fluid bearing for supporting impeller 70 so that impeller 70 can rotate lubricatively without contacting suction ring 84.
Meanwhile, some of the pressurized fluid that has flowed into impeller 83 enters into stator can 65 through the gap between motor shaft 63 and upper bush bearing 67b. The fluid that has flowed into stator can 60 cools motor 10. The fluid in stator can 65 reversely rises to flow into impeller chamber 83, and thereafter flows out of impeller chamber 83 together with other pressurized fluid therein through outlet passage 82.
However, according to the prior-art circulating pump constructed as above, since fluid that has flowed into stator can 65 through the gap between motor shaft 63 and upper bush bearing 67b is small in quantity, motor 60 can not be cooled satisfactorily. As such, since heat generated by friction between motor shaft 63 and bearings 67a and 67b is not sufficiently cooled, motor shaft 63 and bearings 67a and 67b are apt to be worn away earlier, and therefore the efficiency of pump 51 decreases and the expected life of pump 51 is shortened.
Also according to the prior-art circulating pump constructed as above, when a substance such as mud enters stator can 65 together with fluid through the gap between motor shaft 63 and upper bush bearing 67b, since the gap between motor shaft 63 and upper bush bearing 67b is quite narrow, the substance that has entered thereinto is hardly discharged to impeller chamber 63 again. That is, the substance remains in the stator can 65. At this time, if the substance gets in between motor shaft 63 and lower bush bearing 67a, a lubricative rotation of motor shaft 63 can be obstructed. Especially, if pump 51 is left not to be used for a long time, the substance will solidify so the rotation of motor shaft 63 could be impossible.